Bitumen is a viscous liquid or a solid consisting essentially of hydrocarbons and their derivatives. It is soluble in trichloroethylene and softens gradually when heated. Bitumen is combined with aggregate and filler to form asphalt, which is used to pave roads or other surfaces.
Almost 30 million tons of crumb rubbers are annually generated in almost all parts of the world. Polymers are generally classified as thermoplastics and thermosets. Thermoplastic polymers can generally be melted and recycled using heating and remoulding processes. Thermoset polymers are cross-linked and, once they are set, the simple approach of melting and reforming into a new shape does not apply to them. Recycling of thermoset polymers is thus a challenging technical problem. Vulcanized rubber materials are thermoset polymers, and crumb rubber represents the largest stream of waste rubber materials and for the most part, these are inefficiently used or disposed of in landfills.
In parallel, the disposal of plastic water bottles, which are generated in very large quantities, is presently a large social and economic issue because of its bulkiness and the environmental degradation caused by the extremely long decomposition period of plastic.
PET products are excellent candidates for thermal recycling; its by-products are versatile and highly marketable. Plastic manufacturers do not wish to invest substantial resources in new capital equipment to produce new PET polymer material. Existing recycling facilities have insufficient capacity to process the huge amounts of waste generated. The resulting demand for recycled PET material is three times over the existing supply. High availability of lower priced recycled PET is a significant economic consideration in the overall pricing of the finished product. It is neither environmentally biodegradable nor compostable, and thus suffers from disposal problems. Recycling has become a viable alternative to the long-term accumulation of garbage, and there is substantial availability of recyclable PET waste. For example, post-consumer PET derived from soft drink bottles is available in bulk for relatively low cost. Bottle-grade PET is known to be of high quality among the various PET grades, and is available particularly as washed flakes. There are major incentives from environmental perspectives and governmental regulatory directives to find new and improved uses for PET waste.
More attention has been focused on reusing crumb rubbers in the past few years, but the current applications are generally limited to “low value” applications. Understanding the present markets for scrap tyres is a key to continuation and expansion of the recycling efforts toward higher value added uses of these materials.
Crumb rubber, particles of rubber typically obtained from used vehicle tyres, can be incorporated into bitumen. This is a sustainable means of disposing of the crumb rubber and also improves the properties of the bitumen. The crumb rubber is mechanically dispersed in the bitumen. However, during storage the crumb rubber can settle in the bitumen matrix, leading to an inhomogeneous dispersion. Such dispersions can be difficult to transport as it is difficult to pump such dispersions between storage vessels and delivery vehicles. Therefore it is desirable to improve the storage stability of the crumb rubber modified bitumen.
Several composition have been developed in prior art to enhance storage stability of crumb rubber modified bitumen.
U.S. Pat. No. 5,704,971A discloses an improved asphalt composition for pavement and a method for producing the same is characterized by mixing peroxide with crumb rubber to modify the crumb rubber so that it mixes more evenly with the asphalt when added thereto. A compatibilizer/polymer is also added to the asphalt. The resulting composition is homogeneous and demonstrates improved settling and rheological properties at high and low temperatures.
PCT application WO 2010023173A1 discloses a bitumen composition comprising crumb rubber, a polymer comprising glycidyl functional groups and wax. The bitumen composition can be used to prepare asphalt mixtures.
U.S. Pat. No. 6,478,951B1 discloses compatibilizer and process for use in making crumb rubber modified asphalt. The compatibilizer causes the crumb rubber to completely interact with the asphalt, thereby improving the rheological properties of the asphalt and reducing the tendency of pavement made with the asphalt to ravel. The compatibilizer has as its reactive component one or more glycidyl groups; its polymeric backbone can be ethylenic, styrenic, or acrylic or ethylene vinyl acetate (EVA).
U.S. Pat. No. 5,762,700 patent discloses the catalytic process for producing free radicals on crumb rubber by treating the crumb rubber with hydrogen peroxide in the presence of a catalyst such as Fenton's reagent, dioxomolybdenum bis(acetylacetonate), cobalt salt, tall oil, p-toluene sulfonic acid (PTSA), and others.
EP2055745 discloses a composition which comprises bitumen, crumb rubber, a polymer which can be vulcanized and a vulcanizing agent. Additionally, this composition may also comprise an accelerating agent of said vulcanization.